Strictly non-blocking switch core having optimized switching architecture based on reciprocity conditions

ABSTRACT

A switch core is set forth that comprises a plurality of duplex switches that are interconnected with a interconnection fabric to implement, for example, strictly non-blocking operation of the switch core for reciprocal traffic. In one embodiment, an N-way reciprocal switch is implemented. The N-way reciprocal switch comprises a plurality of duplex switches numbering N of at least a 1×(N−1) switch type (e.g., the duplex switches have at least N−1 ports available for connection to implement the interconnection fabric). The interconnection fabric interconnects the plurality of duplex switches so that each duplex switch is connected to every other duplex switch used in the interconnection fabric by a single connection. A similar an architecture using switches numbering N of at least a 1×N switch type are also set forth. Still further, a plurality of duplex switches are used to implement an (n,m)-way switch that, in turn, can be used to construct a recursive LM-way switch core and/or recursively expand an existing Clos switch core.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of non-provisional patentapplication, application Ser. No. 11/234,497, filed on Sep. 23, 2005,now U.S. Pat. No. 7,224,861, which is a continuation of non-provisionalpatent application, application Ser. No. 10/897,642, filed on Jul. 23,2004, now U.S. Pat. No. 6,985,653, which is a continuation ofnon-provisional patent application, application Ser. No. 10/353,425,filed on Jan. 29, 2003, now U.S. Pat. No. 6,785,438, which is acontinuation of non-provisional patent application, application Ser. No.10/003,127, filed on Nov. 2, 2001, now U.S. Pat. No. 6,591,028, which isa continuation of non-provisional patent application, application Ser.No. 09/143,335, filed on Sep. 4, 1998, now U.S. Pat. No. 6,366,713.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

Optical switches and switching architectures are used in opticalnetworks for a variety of applications. One application of opticalswitches is in provisioning of light paths. In this application, theswitches are used to form optical cross-connect architectures, which canbe readily reconfigured to support new light paths. In this application,the switches are replacements for manual fiber patch panels. As such,switches with millisecond switching times are acceptable. The challengewith respect to such applications is to realize large switch sizes.

At the heart of the optical switch is the switch core. In terms ofswitching function, switch cores may be characterized as either blockingor non-blocking architectures. A switch core architecture is said to benon-blocking if any unused input port can be connected to any unusedoutput port. Thus a non-blocking switch core is capable of realizingevery interconnection pattern between the inputs and the outputs. Ifsome interconnection patterns cannot be realized, the switch is said tobe blocking.

A popular architecture for building large non-integrated switch cores isthe Spanke architecture illustrated in FIG. 1. In accordance with theSpanke architecture, an N×N switch is made by combining N switches ofthe 1×N switch type along with N switches of the N×1 switch type, asillustrated. The Spanke architecture results in a strictly non-blockingswitch core architecture that requires 2N switches. The switchillustrated in FIG. 1 is a 4×4 switch core.

The increasing popularity of optical networks has resulted in the needfor larger optical switch cores, thereby increasing the number of inputand output channels (N). Since, in accordance with the formula above,the total number of switches used as well as the size of each switch inthe Spanke switch core architecture increases substantially as thenumber of input and output channels increases, the cost of providing alarge switch is significant and, in some instances, prohibitive.

The present inventors have recognized the reciprocal nature of theconnections in a typical optical switch core employed in a conventionaloptical network. These reciprocity conditions have been used by thepresent inventors to provide a strictly non-blocking optical switch corearchitecture that significantly reduces the number of switches that arerequired to construct the switch core.

BRIEF SUMMARY OF THE INVENTION

A switch core is set forth that comprises a plurality of duplex switchesthat are interconnected with an interconnection fabric to implement, forexample, strictly non-blocking operation of the switch core forreciprocal traffic. In one embodiment, an N-way reciprocal switch isimplemented. The N-way reciprocal switch comprises a plurality of duplexswitches numbering N of at least a 1×(N−1) switch type (e.g., the duplexswitches have at least N−1 ports available for connection to implementthe interconnection fabric). The interconnection fabric interconnectsthe plurality of duplex switches so that each duplex switch is connectedto every other duplex switch used in the interconnection fabric by asingle connection. Such an architecture may also be used to implement aswitch that is not strictly non-blocking.

In a second embodiment, an LM multi-stage reciprocal switch core havingrecursive properties and corresponding (n,m)-way switches are set forth.The LM multi-stage reciprocal switch core is comprised of a plurality ofM-way reciprocal switches numbering at least 2L−1. Each of the pluralityof M-way reciprocal switches is implemented as an N-way reciprocalswitch described above, where N=M. A plurality of (L,2L−1)-wayreciprocal switches numbering M are also used. The multi-stage LMreciprocal switch is itself an LM-way reciprocal switch that can be usedto recursively build larger switches. For example, the LM reciprocalcore switch can be used to implement a larger L₁M₁ multi-stage switch inwhich M₁=LM.

Alternatively, or in addition, the M-way switches used to build the LMswitch core can also be multi-stage in nature and built from smallerrecursive components; i.e., from (j,2j−1)-way switches and (M/j)-wayswitches.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a Spanke switch.

FIG. 2 is a schematic block diagram of a non-square rectangular Spankeswitch core.

FIGS. 3A and 3B are schematic block diagram of N-way reciprocal switchesconstructed in accordance with the present invention.

FIG. 4 is a block diagram of a 1×k duplex switch

FIGS. 5A and 5B are block diagrams of 1×k duplex switches constructedfrom smaller order duplex switches.

FIGS. 6A and 6B are schematic block diagrams of various embodiments of(n,m)-way reciprocal switches constructed in accordance with the presentinvention.

FIG. 7 is a schematic block diagram of an LM×LM non-blocking, Closswitch core.

FIG. 8 is a schematic block diagram of an LM port reciprocal switch coreconstructed in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the Spanke switch architecture illustrated in FIG. 1 for an N×Nswitch, theme are two columns of switches: a left input column of 1×Ntypes switches, shown generally at 10, and a right output column of N×1type switches, shown generally at 15. The column of switches 10 functionas input ports that accept external traffic and direct that trafficthrough the interconnection fabric, shown generally at 17, while thecolumn of switches 15 function as output ports that provide the switchedtraffic to an external device.

FIG. 1 also illustrates the case where reciprocity exists for a pathconnecting the “eastbound” signal at input port 20 to the output port at25. In accordance with this reciprocity condition, the corresponding“westbound” signal at input port 30 is connected to the output port 35.In a more general sense, reciprocity exists if input port A connects itstraffic to output port B whenever input port B connects its traffic tooutput port A.

The present inventors have recognized that, under such reciprocal pathconditions, the port position used by an input switch in the left inputcolumn 10 to direct the traffic through the interconnection fabricdirectly corresponds to the interconnection fabric port position of thecorresponding output switch of the right output column 15 (e.g., fabricport 4 of input switch 20 is provided to the output switch 25 which isin the fourth position of the right output column 15, while fabric port1 of input switch 30 is provided to output switch 35 which is in thefirst position of the right output column 15).

The reciprocity condition has several interesting consequences. In theswitch core of FIG. 1, switch 20 and switch 35 are doing the same thing:they are both set on fabric port position 4. The present inventors haverecognized that this means that the switches 20 and 35 can beimplemented as the same physical switch with separate beams of lightpassing in opposite directions through common lenses or mirrors disposedinside the switch. As such, depending on the specific construction ofthe individual switches, the same actuators, mirrors, lenses, etc., thatconstitute the left-to-right connection through input switch 20 can beduplicated to carry a right-to-left connection by employing a second setof optics in which the second set of optics constitutes the outputswitch 35. In some cases, a second set of optics is not needed. In suchinstances, the same set of optics can carry two parallel beams going inopposite directions. In effect, the it and output switches are collapsedinto a single 1×N duplex switch having two beams of light carryingtraffic in opposite directions. For one direction, such a duplex switchis acting like an input 1×N switch, and for the other direction as anoutput N×1 switch.

A square N×N switch architecture is not the only type of architecture inwhich reciprocity may exist and used to an advantage. FIG. 2 illustratesa non-square rectangular Spanke switch core in which not all inputs areconnected to all outputs. Unused paths are indicated by dashed lines.Such a switch, however, can still take advantage of the savingsassociated with reciprocity. In a reciprocal connection condition, inputswitch 40, as above, is sending the “eastbound” traffic through thefabric 17 from the fabric port at position 4 to the fabric port atposition 1 of the output switch 45 in the fourth position. Likewise,input switch 50 sends the corresponding “westbound” traffic through thefabric 17 from the fabric port at position 1 to the fabric port atposition 4 to the output switch 55 in the fit position. Once again, suchreciprocity means that each input switch can be combined with thecorresponding output switch by means of double light paths throughcommon lenses or mirrors. The principal difference between the switchcore of FIG. 1 and the switch core of FIG. 2 is that certain paths inthe core of FIG. 2 are not utilized as indicated by the thin dashedlines.

Since much of the cost of most switches typically centers on theactuation mechanism and mirror or lens employed in the switch, using aswitch that is collapsed so that these components are common to bothlight paths can approach a 2-to-1 savings, provided that the paths arereciprocal. It has been found, that the typical networks, such as SONETrarely, if ever, violate this reciprocal condition.

Application of the foregoing principles to design large optical switchcores results in a number of different switch core architectures thatare optimized when compared to their traditionally designed switch corecounterparts. The optimized switch core architectures are comprised ofone or more stages of duplex switch modules, such as the single moduleshown at 60 of FIG. 3. Each duplex switch module 60 is comprised ofindividual 1×k duplex switches, such as at 65 of FIGS. 3A and 4, where kmay vary from switch to switch within the module 60. As noted above, a1×k duplex switch generally functions as a traditional 1×k switch, butallows signal traffic to flow in both directions of the switch therebyallowing the switch to function as both an input and output switchsharing common optical components for the input and output paths.

One embodiment of a switch core architecture that uses the foregoingprinciples to reduce the complexity of the switching architecture isillustrated in FIG. 3A. As illustrated, the optical switch core includesa single N-way duplex module 60 comprised of N switches 65 of the1×(N−1) duplex switch type (i.e., k−N−1). Such a switch core 60 allowsduplex connections between any pair of free ports regardless of existingconnections and, as such, is similar to the N×N strictly non-blockingSpanke switch architecture of FIG. 1. However, switch core 60 is onlystrictly non-blocking for reciprocal traffic.

In the embodiment shown in FIG. 3A, module 60 is a 4-way reciprocalswitch core and, as such, uses 4 duplex switches of the 1×3 switch type.The 1×3 duplex switches are interconnected to form the fabric of the4-way reciprocal switch core in the manner forth in Table 1.

TABLE 1 Switch Position Fabric Port Internal Port Connection 1 1 FabricPort 1 Of Switch at Switch Position 2 1 2 Fabric Port 1 Of Switch atSwitch Position 3 1 3 Fabric Port 1 Of Switch at Switch Position 4 2 1Fabric Port 1 Of Switch at Switch Position 1 2 2 Fabric Port 2 Of Switchat Switch Position 3 2 3 Fabric Port 2 Of Switch at Switch Position 4 31 Fabric Port 2 Of Switch at Switch Position 1 3 2 Fabric Port 2 OfSwitch at Switch Position 2 3 3 Fabric Port 3 Of Switch at SwitchPosition 4 4 1 Fabric Port 3 Of Switch at Switch Position 1 4 2 FabricPort 3 Of Switch at Switch Position 2 4 3 Fabric Port 3 Of Switch atSwitch Position 3In accordance with the foregoing interconnections of the duplex switchesof the 1×(N−1) switch type, each switch is connected to every otherswitch by a single fabric interconnection. Many other permutations arepossible for interconnecting the switches. The principal criterion is toconnect each switch to every other switch.

If 1×4 duplex switches (e.g., 1×(N) type duplex switches) are used, astrictly non-blocking switch architecture having loop-back may beimplemented. Such an architecture is illustrated in FIG. 3B.Interconnections between the duplex switches in such an architecture areas set forth in Table 2.

TABLE 2 Switch Position Internal Port Position Internal Port Connection1 1 Loop-back 1 2 Internal Port 1 Of Switch at Switch Position 2 1 3Internal Port 1 Of Switch at Switch Position 3 1 4 Internal Port 1 OfSwitch at Switch Position 4 2 1 Internal Port 2 Of Switch at SwitchPosition 1 2 2 Loop-back 2 3 Internal Port 2 Of Switch at SwitchPosition 3 2 4 Internal Port 2 Of Switch at Switch Position 4 3 1Internal Port 3 Of Switch at Switch Position 1 3 2 Internal Port 3 OfSwitch at Switch Position 2 3 3 Loop-back 3 4 Internal Port 3 Of Switchat Switch Position 4 4 1 Internal Port 4 Of Switch at Switch Position 14 2 Internal Port 4 Of Switch at Switch Position 2 4 3 Internal Port 4Of Switch at Switch Position 3 4 4 Loop-backIt will be recognized in view of the foregoing description that otherpermutations for the interconnect fabric are also possible. Theprincipal goal is to connect each switch to every other switch by atleast a single fabric interconnection. The specific interconnections ofthe duplex switches of the 1×N switch type in Table 2, however, can begeneralized in the following manner. Let X represent the switch positionof the duplex switch in the overall switch architecture, where X is anumber from, for example, 1 through N. Let Y represent the fabric portof switch where Y is a number from, for example, 1 through N. Tointerconnect the duplex switches to form a strictly non-blocking, N-wayswitch for reciprocal traffic, each fabric port Y of each switch X isconnected to the fabric port X of switch Y when X≠Y, and wherein eachpath Y may optionally be used for loop-back when X=Y. Again, suchinterconnections are made starting with switch X=1 until each duplexswitch is connected to every other duplex switch of the interconnectionfabric by a single connection.

FIGS. 5A and 5B illustrates various manners in which duplex switches ofa lesser order may be cascaded to form larger 1×k duplex switches, suchas the one shown at 65 of FIG. 4. More particularly, FIG. 5A illustratesa 1×12 reciprocal switch at 65 that is comprised of a single 1×3reciprocal switch 67 that is cascaded with a further group of three 1×4reciprocal switches 69. In like fashion, FIG. 5B illustrates a 1×9reciprocal switch at 65 that is comprised of a single 1×3 switch 71 thatis cascaded with a further group of three 1×3 reciprocal switches 73. Itwill be recognized that other 1×k reciprocal switches may be formed fromlesser order reciprocal switches. In such instances, the overallswitching architecture may be optimized by using as few of the lowerorder or reciprocal switch types as possible, thereby reducing thenumber of component types required to manufacture the overall switch.

Other switch architectures may be implemented in accordance with theforegoing principles. One such architecture is the (n,m)-way module,shown generally at 80 of FIG. 6A. The (n,m)-way module 80 is similar infunctionality to the n-way module 60 of FIG. 3, except that it has n+mduplex switches. The duplex switches are logically divided into twogroups: a first group of switches 85 numbering n and a second group ofswitches 90 numbering m. Only the first group of switches 85 can formduplex connections to any other port in the module 80. The second groupof switches 90 can only connect to the switches of the first group 85.

In the preferred construction of the (n,m)-way module 80, a total of nduplex switches 95 of the 1×(n+m−1) type are employed for the firstgroup of switches 85 and a total of m duplex switches 100 of the 1×ntype are employed for the second group of switches 90. To effect thestated operation of the first group of ports 85, the fabric ports ofeach switch 95 of the first group of switches 85 are connected to thefabric ports of every other switch in the module 80. This insures thatthe first group of switches 85 is allowed to form duplex connections toany other switch in the module 80. To effect the stated operation of thesecond group of switches 90, each fabric port of each switch 100 in thesecond group of switches 90 is connected only to a respective fabricport of the first group of switches 95. As such, each duplex switch ofthe first group of switches 85 is connected to every other switch by asingle interconnection, while each duplex switch of the second group ofswitches 90 is interconnected to each of the first group of switches 85by a single interconnection without further interconnection to any ofthe switches 100 of the second group.

The exemplary module 80 of FIG. 6A illustrates construction of a(3,4)-way module. Interconnections between the duplex switches in theillustrated architecture are as set forth in Table 3. Again, variouspermutations may be employed.

TABLE 3 Switch Position Fabric Port Position Fabric Port ConnectionFirst Group - 1 1 Fabric Port 1 Of First Group Switch at Switch Position2 First Group - 1 2 Fabric Port 1 Of First Group Switch at SwitchPosition 3 First Group - 1 3 Fabric Port 1 Of Second Group Switch atSwitch Position 1 First Group - 1 4 Fabric Port 1 Of Second Group Switchat Switch Position 2 First Group - 1 5 Fabric Port 1 Of Second GroupSwitch at Switch Position 3 First Group - 1 6 Fabric Port 1 Of SecondGroup Switch at Switch Position 4 First Group - 2 1 Fabric Port 1 OfFirst Group Switch at Switch Position 1 First Group - 2 2 Fabric Port 2Of First Group Switch at Switch Position 3 First Group - 2 3 Fabric Port2 Of Second Group Switch at Switch Position 1 First Group - 2 4 FabricPort 2 Of Second Group Switch at Switch Position 2 First Group - 2 5Fabric Port 2 Of Second Group Switch at Switch Position 3 First Group -2 6 Fabric Port 2 Of Second Group Switch at Switch Position 4 FirstGroup - 3 1 Fabric Port 2 Of First Group Switch at Switch Position 1First Group - 3 2 Fabric Port 2 Of First Group Switch at Switch Position2 First Group - 3 3 Fabric Port 3 Of Second Group Switch at SwitchPosition 1 First Group - 3 4 Fabric Port 3 Of Second Group Switch atSwitch Position 2 First Group - 3 5 Fabric Port 3 Of Second Group Switchat Switch Position 3 First Group - 3 6 Fabric Port 3 Of Second GroupSwitch at Switch Position 4

An alternative construction of an (n,m)-way switch is illustrated inFIG. 6B. In the specific exemplary alternative construction shown, theduplex switches are connected to form a (3,3)-way switch. As above, theswitch shown generally at 81, comprises a first group of duplex switches86 and a second group of duplex switches 87. Only the first group ofswitches 86 can form duplex connections-to-any other port in the module81. The second group of switches 87 can only connect to the switches ofthe first group 86. To effect duplex connection between the ports of thefirst group of switches 86, an n-way switch 88 is used to interconnectthe fabric ports of the duplex switches of the first group 86. Theadvantage of the alternative structure is that module 88 is simply ann-way switch. By choosing the cardinality of the individual modules ofthe final overall switch architecture, the number of different parttypes used in the switch maybe reduced.

The architecture of the n-way reciprocal and (n,m)-way reciprocalmodules 60, 80 set forth in FIGS. 3 and 6A (6B), respectively, may becombined to emulate a Clos-like switching core. For comparison, athree-stage LM×LM Clos switching core is illustrated in FIG. 7. Asillustrated, there are three groups of switches 110, 115, and 120. Thefirst group of switches 110 is comprised of conventional, unidirectionalswitches 125 numbering M of the L×2L−1 switch type. The second group ofswitches 115 is comprised of conventional, unidirectional switches 130numbering 2L−1 of the M×M switch type. The third group of switches 120is comprised of conventional, unidirectional switches 135 numbering M ofthe 2L−1×L switch type.

The interaction of the switch groups 110, 115, and 120 and operation ofthe resultant switching core are well-known. A significant property ofthe Clos switching structure is its recursive nature. This recursiveproperty allows a larger Clos switch to be formed from a plurality ofsmaller Clos switch structures.

FIG. 8 illustrates a strictly non-blocking core switch 150 having fewerswitches, yet having the same functionality as the LM×LM Clos switch ofFIG. 7, except that such functionality is limited to reciprocal traffic.The switch core 150 is implemented using a plurality of switchingmodules of the types described above in connection with FIGS. 3 (or 5)and 6. As illustrated, the switch core 150 employs two groups ofswitching modules 155 and 160. The first group of modules 155 iscomprised of a plurality of (L,2L−1)-way modules 165 numbering M. The(L,2L−1)-way modules 165 are designed in accordance with the principlesof the (n,m)-way reciprocal switching module described above inconnection with FIG. 6, where n=L and m=2L−1. The second group ofmodules 160 is comprised of a plurality of M-way reciprocal switchingmodules 170 numbering 2L−1. The M-way modules 170 are designed inaccordance with the principles of the N-way reciprocal switching moduledescribed above in connection with FIG. 3A, where N=M.

The modules 165 of the first group of modules 155 are connected to themodules 170 of the second group of modules 160 so that tic at theexternally disposed I/O ports 180 handle reciprocal traffic in astrictly non-blocking manner. To this end, the fabric port at position jof the module 165 at position k of the first group of modules 155 isconnected to the fabric port at position k of the module 170 at positionj of the second group of modules 160. Examples of this interconnectionare set forth in Table 4.

TABLE 4 Module Position Fabric Port Position Fabric Port ConnectionFirst Group - 1 1 Fabric Port 1 Of Module of Second Group at Position 1First Group - 1 2 Fabric Port 1 Of Module of Second Group at Position 2First Group - 1 3 Fabric Port 1 Of Module of Second Group at Position 3. . . . . . . . . First Group - 1 L Fabric Port 1 Of Module of SecondGroup at Position L First Group - 2 1 Fabric Port 2 Of Second GroupSwitch at Switch Position 1 . . . . . . . . . First Group - 2 L FabricPort 2 Of Second Group Switch at Switch Position L . . . . . . . . .First Group - M L Fabric Port M Of Second Group Switch at SwitchPosition L

Again, there are areas permutations that will work as long as eachmodule of the first group is connected to every module in the secondgroup. The LM-way reciprocal core 150 appears to emulate a foldedversion of the Clos architecture of FIG. 7. The second group of modules160 of the LM-way reciprocal core is simply the left half of the middleClos stage 115 while the first group of modules 155 of the reciprocalcore 150 takes on the role of both outer stages 110 and 120 of the Closarchitecture.

Table 5 summarizes the complexity of the Clos switch core of FIG. 7 andthe switch core 150 in terms of the number of each elemental switch typeemployed to implement the core, assuming each module in FIGS. 7 and 8 isimplemented using 1×X switch and that the (n,M)-way modules areimplemented as shown in FIG. 6A:

TABLE 5A LM-WAY LM × LM RECIPROCAL CORE NON-BLOCKING CLOS No. Of SimplexDuplex Switch Type Switches Switch Type No. Of Switches 1 × 3L − 1 LM 1× 3L − 1 None 1 × 2L − 1 None 1 × 2L − 1 2ML 1 × L M(2L − 1) 1 × L 2M(2L− 1) 1 × M − 1 M(2L − 1) 1 × M 2M(2L − 1)

The LM-way reciprocal core 150 employs half as many elemental switchesas the traditional Clos core. In the LM-way reciprocal core 150,however, the 1×2L−1 switch type is replaced with a 1×3L−1 switch typefor implementing the (L,2L−1)-way modules 165. Although the elementalswitches of the LM-way reciprocal core 150 are duplex switches which aregenerally more costly than traditional switches, the incremental costsfor such duplex switches will not generally exceed the savings resultingfrom the reduced number of elemental duplex switches that are utilized.Further savings are realized from the present invention in terms ofpower and so requirements as well.

Similar efficiencies are realized when it is assumed that the (n,m)-waymodules of switch 150 are implemented as shown in FIG. 6B. Such acomparison to the Clos switch is set forth in Table 5B.

TABLE 5B LM-WAY LM × LM RECIPROCAL CORE NON-BLOCKING CLOS No. Of SimplexDuplex Switch Type Switches Switch Type No. Of Switches 1 × 3L − 1 None1 × 3L − 1 None 1 × 2L − 1 LM 1 × 2L − 1 2ML 1 × L M(2L − 1) + 1 × L2M(2L − 1) LM 1 × M − 1 M(2L − 1) 1 × M 2M(2L − 1)As illustrated, the LM-way switch 150, when using the architecture ofFIG. 6B, uses half as many 1×2L−1 and 1×M the switches, andapproximately ¾ the number of 1×L switches. Although the elementalswitches used by the reciprocal core are duplex switches, and those ofthe Clos architecture are simplex switches, a cost savings can still berealized if the cost of a duplex switch is less than twice the cost ofthe simplex switch counterpart.

The traditional Clos architecture is a recursive architecture; i.e., alarger Clos core can be built using one or more smaller Clos cores inthe middle stages. Similarly, the LM-way reciprocal core architecture isalso recursive. The LM-way reciprocal core 150 has the functionality ofa LM-way duplex module. As such, it can be utilized as the second stagemodule of a larger core. For example, a 256-port reciprocal core can bemade by using three LM-way reciprocal cores of 128 ports each as thesecond group of modules 160 in the architecture of FIG. 8, and 128(2,3)-way modules as the first group of modules 155. Such recursivenessfacilitates ready expansion of an existing switch thereby allowing auser to upgrade their switching system without disposing of existinghardware. Indeed, the LM-way reciprocal core 150 may bemodular—upgrading of the core merely comprising the addition of one ormore further modules.

The first group of switches 155 of FIG. 8 can also be used to expand anexisting LM×LM non-reciprocal, non-blocking core, such as the oneillustrated in FIG. 7. In such instances, the second group of switches160 of FIG. 8 are replaced by a plurality of LM×LM non-blocking cores,such as those illustrated in FIG. 7. This allows the (n,m)-wayarchitectures to expand existing non-reciprocal core architecturesthereby eliminating the need to purchase new switching cores to replacethe older, existing switching cores.

Numerous modifications may be made to the foregoing system withoutdeparting from the basic teachings thereof. Although the presentinvention has been described substantial detail with reference to one ormore specific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the scope and spiritof the invention as set forth in the appended claims.

1. A method of managing a switch core, comprising: arranging N duplexswitches by connecting each of the N duplex switches to every other ofthe N duplex switches; and adapting each of the N duplex switches soloop-back a signal path from at least one port in each of the N duplexswitches to the at least one port.
 2. The method of claim 1, whereinadapting each of the N duplex switches to loop-back the signal pathcomprises arranging optics within each of the N duplex switches totransmit the signal path from the at least one port in each of the Nduplex switches to the at least one port.
 3. The method of claim 1,wherein the signal path which is to be looped-back is reciprocal.
 4. Themethod of claim 1, wherein connecting each of the N duplex switches toevery other of the N duplex switches comprises arranging optics withineach of the N duplex switches to transmit additional signal pathsbetween ports of the N duplex switches.
 5. The method of claim 4,wherein the additional signal paths are reciprocal.
 6. The method ofclaim 1, further comprising arranging the N duplex switches to allowsignal traffic to flow into and out of the N duplex switches.
 7. Aswitch core, comprising: N duplex switches, wherein each of the N duplexswitches is adapted to be connected to every other of the N duplexswitches and at least one port in each of the N duplex switches isadapted to loop-back a signal path from the at least one port to the atleast one port.
 8. The switch core of claim 7, wherein the N duplexswitches are at least a 1×N switch type.
 9. The switch core of claim 7,further comprising optics within the N duplex switches which are adaptedto transmit signals between the ports of the N duplex switches.
 10. Theswitch core of claim 7, wherein the optics are at least one ofactuators, mirrors and lenses.
 11. The switch core of claim 7, whereinthe N duplex switches are adapted to allow signal traffic to flow intoand out of the N duplex switches.
 12. The switch core of claim 7,wherein the at least one port in each of the N duplex switches isadapted to loop-back a signal path by being adapted to connect thesignal path from the at least one port to the at least one port.
 13. Theswitch core of claim 7, wherein each of the N duplex switches is adaptedto be connected to every other of the N duplex switches by being adaptedto connect signal path between ports of the N duplex switches.